Propylene ethylene polymers

ABSTRACT

Ethylene propylene copolymers, substantially free of diene, are described. The copolymers will have a uniform distribution of both tacticity and comonomer between copolymer chains. Further, the copolymers will exhibit a statistically insignificant intramolecular difference of tacticity. The copolymers are made in the presence of a metallocene catalyst.

[0001] This is a continuation-in-part of Ser. No. 08/910,001, filed Aug.12, 1997; Ser. No. 09/108,467, filed Jul. 1, 1998; Ser. No. 09/342,854,filed Jun. 29, 1999; and Ser. No. 09/346,460, filed Jul. 1, 1999, whichis a continuation-in-part of Ser. No. 09/108,772, filed Jul. 2, 1998,now abandoned; the disclosures of these documents are incorporatedherein by reference.

FIELD

[0002] Embodiments of the present invention include copolymers ofethylene and propylene, in the substantial absence of dienes. Morespecifically, the copolymers are made in a process that employs a singlereactor, in steady state.

BACKGROUND

[0003] Ethylene propylene copolymers made with metallocene catalysts areknown. Many such copolymers are intermolecularly heterogeneous in termsof tacticity, composition (weight percent comonomers) or both. Further,such polymers may also, or in the alternative, be compositionallyheterogeneous within a polymer chain. Such characteristics may be, butare not always, the result of multiple reactor schemes or sequentialaddition of polymer.

[0004] The elasticity, flexural modulus and tensile strength of suchcopolymers, when considered in the aggregate, may not reach asatisfactory level for use in commercial elastomeric operation.

[0005] U.S. Pat. No. 5,747,621 suggests fractionable reactor blendpolypropylenes, directly obtainable from the polymerization reaction ofpropylene having 30 to 90% by weight of a boiling n-heptane fraction,soluble in xylene at 135° C. In Table 2 of this document, the onlyfractionation disclosed, each of the solvents appears to be at itsboiling point. Further, reference to this table shows that thediethyl-ether fraction has no melting point (amorphous).

[0006] In the journal articles Science, Vol. 267, pp 217-219 (1995);Macromolecules, Vol. 31, pp 6908-6916 (1998); and Macromolecules, Vol.32, pp 8283-8290, pp 3334-3340 and pp 8100-8106, propylene polymers withsimilar characteristics as those disclosed in the above discussed U.S.Pat. No. 5,747,621 are made and fractionated. The polymers are made withbis(aryl indenyl) or bisindenyl metallocene catalysts. In these journalarticles, these polymers are fractionated in boiling ether and heptane,leaving a portion of the polymer insoluble in either. The polypropylenesare stated to be compositionally heterogeneous in terms of tacticity andmolecular weight.

[0007] U.S. Pat. No. 5,504,172 suggests a propylene elastomer that hasproperties such that:

[0008] (a) the elastomer contains propylene units in an amount of 50 to95% by mol and ethylene units in an amount of 5 to 50% by mol;

[0009] (b) a triad tacticity of three propylene units-chains consistingof head-to-tail bonds, as measured by ¹³C NMR, is not less than 90.0%;and

[0010] (c) a proportion of inversely inserted propylene units based onthe 2,1-insertion of a propylene monomer in all propylene insertions, asmeasured by ¹³C NMR, is not less than 0.5%, and a proportion ofinversely inserted propylene units based on the 1,3-insertion of apropylene monomer, as measured by ¹³C NMR, is not more than 0.05%.

[0011] U.S. Pat. No. 5,391,629 suggests block and tapered copolymers ofethylene with an α-olefin. The copolymers are made by a process ofsequentially contacting ethylene with an α-olefin monomer in thepresence of an activated cyclopentadienyl catalyst system.

[0012] EP 0 374 695 suggests ethylene-propylene copolymers and a processfor preparing them. The copolymers have a reactivity ratio product,r₁r₂, between 0.5 and 1.5 and an isotactic index greater than 0 percent.The copolymers are produced in the presence of a homogeneous chiralcatalyst and an alumoxane co-catalyst.

[0013] There is a commercial need therefore for an ethylene propylenecopolymer that will show a melting point and an excellent balance ofelasticity, flexural modulus and tensile strength.

SUMMARY

[0014] We have discovered that ethylene-propylene copolymers, whenproduced in the presence of a metallocene catalyst and an activator, ina single steady state reactor, show a surprising and unexpected balanceof flexural modulus, tensile strength and elasticity. Moreover, theseand other properties of the copolymers show surprising differencesrelative to conventional polymer blends, such as blends of isotacticpolypropylene and ethylene-propylene copolymers.

[0015] In one embodiment, the copolymer includes from a lower limit of5% or 6% or 8% or 10% by weight to an upper limit of 20% or 25% byweight ethylene-derived units, and from a lower limit of 75% or 80% byweight to an upper limit of 95% or 94% or 92% or 90% by weightpropylene-derived units, the percentages by weight based on the totalweight of propylene- and ethylene-derived units. The copolymer issubstantially free of diene-derived units.

[0016] In various embodiments, features of the copolymers include someor all of the following characteristics, where ranges from any recitedupper limit to any recited lower limit are contemplated:

[0017] (i) a melting point ranging from an upper limit of less than 110°C., or less than 90° C., or less than 80° C., or less than 70° C., to alower limit of greater than 25° C., or greater than 35° C., or greaterthan 40° C., or greater than 45° C.;

[0018] (ii) a relationship of elasticity to 500% tensile modulus suchthat

Elasticity ≦0.935M+12, or

Elasticity ≦0.935M+6, or

Elasticity ≦0.935M,

[0019] where elasticity is in percent and M is the 500% tensile modulusin megapascal (MPa);

[0020] (iii) a relationship of flexural modulus to 500% tensile modulussuch that

Flexural Modulus ≦4.2e ^(0.27M)+50, or

Flexural Modulus ≦4.2e ^(0.27M)+30, or

Flexural Modulus ≦4.2e ^(0.27M)+10, or

Flexural Modulus ≦4.2e ^(0.27M)+2,

[0021] where flexural modulus is in MPa and M is the 500% tensilemodulus in MPa;

[0022] (iv) a heat of fusion ranging from a lower limit of greater than1.0 joule per gram (J/g), or greater than 1.5 J/g, or greater than 4.0J/g, or greater than 6.0 J/g, or greater than 7.0 J/g, to an upper limitof less than 125 J/g, or less than 100 J/g, or less than 75 J/g, or lessthan 60 J/g, or less than 50 J/g, or less than 40 J/g, or less than 30J/g;.

[0023] (v) a triad tacticity as determined by carbon-13 nuclear magneticresonance (¹³C NMR) of greater than 75%, or greater than 80%, or greaterthan 85%, or greater than 90%;

[0024] (vi) a tacticity index m/r ranging from a lower limit of 4 or 6to an upper limit of 8 or 10 or 12;

[0025] (vii) a proportion of inversely inserted propylene units based on2,1 insertion of propylene monomer in all propylene insertions, asmeasured by ¹³C NMR, of greater than 0.5% or greater than 0.6%;

[0026] (viii) a proportion of inversely inserted propylene units basedon 1,3 insertion of propylene monomer in all propylene insertions, asmeasured by ¹³C NMR, of greater than 0.05%, or greater than 0.06%, orgreater than 0.07%, or greater than 0.08%, or greater than 0.085%;

[0027] (ix) an intermolecular tacticity such that at least X % by weightof the copolymer is soluble in two adjacent temperature fractions of athermal fractionation carried out in hexane in 8° C. increments, where Xis 75, or 80, or 85, or 90, or 95, or 97, or 99;

[0028] (x) a reactivity ratio product r₁r₂ of less than 1.5, or lessthan 1.3, or less than 1.0, or less than 0.8;

[0029] (xi) a molecular weight distribution Mw/Mn ranging from a lowerlimit of 1.5 or 1.8 to an upper limit of 40 or 20 or 10 or 5 or 3;

[0030] (xii) a molecular weight of from 15,000-5,000,000;

[0031] (xiii) a solid state proton nuclear magnetic resonance (¹H NMR)relaxation time of less than 18 milliseconds (ms), or less than 16 ms,or less than 14 ms, or less than 12 ms, or less than 10 ms;

[0032] (xiv) an elasticity as defined herein of less than 30%, or lessthan 20%, or less than 10%, or less than 8%, or less than 5%; and

[0033] (xv) a 500% tensile modulus of greater than 0.5 MPa, or greaterthan 0.8 MPa, or greater than 1.0 MPa, or greater than 2.0 MPa.

[0034] The copolymer be made in the presence of a bridged metallocenecatalyst, in a single steady-state reactor. Thus, in another aspect, thepresent invention is directed to a process for producing anethylene-propylene copolymer having some or all of the above-recitedcharacteristics, by reacting ethylene and propylene in a steady-statereactor under reactive conditions and in the presence of a bridgedmetallocene catalyst.

DESCRIPTION OF THE DRAWINGS

[0035] These and other features, aspects and advantages of embodimentsof our invention will become better understood with reference to thefollowing description, appended claims and accompanying drawings, inwhich:

[0036]FIG. 1 is a plot of the natural log of crystalline intensity (by¹H NMR) versus time in milliseconds; T_(1p) referred to in thisdescription is the slope of the line.

[0037]FIG. 2 is a plot of flexural modulus, in MPa, versus 500% tensilemodulus, in MPa.

[0038]FIG. 3 is a plot of elasticity, in percent, versus 500% tensilemodulus, in MPa.

[0039]FIG. 4 is a plot of melting point (Tm) in ° C., as determined byDSC, versus percent ethylene of copolymers of the invention (trianglesymbols) and blends of isotactic polypropylene with copolymers of theinvention (diamond symbols).

DESCRIPTION

[0040] We contemplate thermoplastic polymer compositions composed of amajority of propylene with a minor amount of ethylene. These polymercompositions include a linear, single homogeneous macromolecularcopolymer structure. These polymers have limited crystallinity due toadjacent isotactic propylene units and have a melting point as describedbelow. They are generally devoid of any substantial intermolecularheterogeneity in tacticity and comonomer composition, and aresubstantially free of diene. They are also devoid of any substantialheterogeneity in intramolecular composition distribution. In addition,these thermoplastic polymer compositions are unexpectedly soft andelastic.

[0041] Copolymer

[0042] Monomers in the Copolymer

[0043] According to an embodiment of the present invention, thecopolymer includes from a lower limit of 5% or 6% or 8% or 10% by weightethylene-derived units to an upper limit of 20% or 25% by weightethylene-derived units. These embodiments also will includepropylene-derived units present in the copolymer in the range of from alower limit of 75% or 80% by weight to an upper limit of 95% or 94% or92% or 90% by weight. These percentages by weight are based on the totalweight of the propylene and ethylene-derived units; i.e., based on thesum of weight percent propylene-derived units and weight percentethylene-derived units being 100%. Within these ranges, these copolymersare mildly crystalline as measured by differential scanning calorimetry(DSC), and are exceptionally soft, while still retaining substantialtensile strength and elasticity. Elasticity, as defined in detailhereinbelow, is a dimensional recovery from elongation for thesecopolymers. At ethylene compositions lower than the above limits for thecopolymer, such polymers are generally crystalline, similar tocrystalline isotactic polypropylene, and while having excellent tensilestrength, they do not have the favorable softness and elasticity. Atethylene compositions higher than the above limits for the copolymercomponent, the copolymer is substantially amorphous. While such amaterial of higher ethylene composition may be soft, these compositionsare weak in tensile strength and poor in elasticity. In summary, suchcopolymers of embodiments of our invention exhibit the softness, tensilestrength and elasticity characteristic of vulcanized rubbers, withoutvulcanization.

[0044] In embodiments of the present invention, we intend that thecopolymers be substantially free of diene-derived units. Dienes arenonconjugated diolefins which may be incorporated in polymers tofacilitate chemical crosslinking reactions. “Substantially free ofdiene” is defined to be less than 1% diene, or less than 0.5% diene, orless than 0.1% diene, or less than 0.05% diene, or equal to 0%. All ofthese percentages are by weight in the copolymer. The presence orabsence of diene can be conventionally determined by infrared techniqueswell known to those skilled in the art.

[0045] Sources of diene include diene monomer added to thepolymerization of ethylene and propylene, or use of diene in catalysts.No matter the source of such dienes, the above outlined limits on theirinclusion in the copolymer are contemplated. Conjugated diene-containingmetallocene catalysts have been suggested for the formation ofcopolymers of olefins. However, polymers made from such catalysts willincorporate the diene from the catalyst, consistent with theincorporation of other monomers in the polymerization.

[0046] Molecular Weight and Polydispersity Index

[0047] Molecular weight distribution (MWD) is a measure of the range ofmolecular weights within a given polymer sample. It is well known thatthe breadth of the MWD can be characterized by the ratios of variousmolecular weight averages, such as the ratio of the weight averagemolecular weight to the number average molecular weight, Mw/Mn, or theratio of the Z-average molecular weight to the weight average molecularweight, Mz/Mw.

[0048] Mz, Mw and Mn can be measured using gel permeation chromatography(GPC), also known as size exclusion chromatography (SEC). This techniqueutilizes an instrument containing columns packed with porous beads, anelution solvent, and detector in order to separate polymer molecules ofdifferent sizes. In a typical measurement, the GPC instrument used is aWaters chromatograph equipped with ultrastyro gel columns operated at145° C. The elution solvent used is trichlorobenzene. The columns arecalibrated using sixteen polystyrene standards of precisely knownmolecular weights. A correlation of polystyrene retention volumeobtained from the standards, to the retention volume of the polymertested yields the polymer molecular weight.

[0049] Average molecular weights M can be computed from the expression:$M = \frac{\sum\limits_{i}{N_{i}M_{i}^{n + 1}}}{\sum\limits_{i}{N_{i}M_{i}^{n}}}$

[0050] where Ni is the number of molecules having a molecular weightM_(i). When n=0, M is the number average molecular weight Mn. When n=1,M is the weight average molecular weight Mw. When n=2, M is theZ-average molecular weight Mz. The desired MWD function (e.g., Mw/Mn orMz/Mw) is the ratio of the corresponding M values. Measurement of M andMWD is well known in the art and is discussed in more detail in, forexample, Slade, P. E. Ed., Polymer Molecular Weights Part II, MarcelDekker, Inc., NY, (1975) 287-368; Rodriguez, F., Principles of PolymerSystems 3rd ed., Hemisphere Pub. Corp., NY, (1989) 155-160; U.S. Pat.No. 4,540,753; Verstrate et al., Macromolecules, vol. 21, (1988) 3360;and references cited therein.

[0051] In embodiments of our invention, a copolymer is included having aweight average molecular weight (Mw) of from 15,000-5,000,000, or from20,000 to 1,000,000 and a molecular weight distribution Mw/Mn (sometimesreferred to as a “polydispersity index” (PDI)) ranging from a lowerlimit of 1.5 or 1.8 to an upper limit of 40 or 20 or 10 or 5 or 3.

[0052] In the measurement of properties ascribed to polymers ofembodiments of our invention, there is a substantial absence of asecondary or tertiary polymer or polymers to form a blend. By“substantial absence” we intend less than 10%, or less than 5%, or lessthan 2.5%, or less than 1%, or 0%, by weight.

[0053] Melting Point and Crystallinity

[0054] The copolymer, according to an embodiment of our invention, has asingle melting point. The copolymer can be a random copolymer ofethylene and propylene having a melting point (Tm) by DifferentialScanning Calorimetry (DSC) ranging from an upper limit of less than 110°C., less than 90° C., less than 80° C., or less than 70° C.; to a lowerlimit of greater than 25° C., or greater than 35° C., or greater than40° C. or greater than 45° C. FIG. 4 shows the melting point ofpropylene-ethylene copolymers of the invention as a function of ethyleneweight percent, i.e., weight percent of ethylene-derived units (trianglesymbols). For comparison, the diamond symbols in FIG. 4 show the meltingpoint of blends of isotactic polypropylene and the inventive copolymersalso as a function of weight percent ethylene. FIG. 4 clearly shows thatcopolymers of the present invention have a lower melting point thanpropylene-ethylene copolymer/isotactic polypropylene blends having thesame weight percent ethylene.

[0055] Embodiments of our invention include copolymers having a heat offusion, as determined by DSC, ranging from a lower limit of greater than1.0 J/g, or greater than 1.5 J/g, or greater than 4.0 J/g, or greaterthan 6.0 J/g, or greater than 7.0 J/g, to an upper limit of less than125 J/g, or less than 100 J/g, or less than 75 J/g, or less than 60 J/g,or less than 50 J/g, or less than 40 J/g, or less than 30 J/g. Withoutwishing to be bound by theory, we believe that the copolymers ofembodiments of our invention have generally isotactic crystallizablepropylene sequences, and the above heats of fusion are believed to bedue to the melting of these crystalline segments.

[0056] Tacticity Index

[0057] The tacticity index, expressed herein as “m/r”, is determined by¹³C nuclear magnetic resonance (NMR). The tacticity index m/r iscalculated as defined in H. N. Cheng, Macromolecules, 17, 1950 (1984).The designation “m” or “r” describes the stereochemistry of pairs ofcontiguous propylene groups, “m” referring to meso and “r” to racemic.An m/r ratio of 1.0 generally describes a syndiotactic polymer, and anm/r ratio of 2.0 an atactic material. An isotactic materialtheoretically may have a ratio approaching infinity, and many by-productatactic polymers have sufficient isotactic content to result in ratiosof greater than 50. Copolymers of embodiments of our invention can havea tacticity index m/r ranging from a lower limit of 4 or 6 to an upperlimit of 8 or 10 or 12.

[0058] Triad tacticity

[0059] An ancillary procedure for the description of the tacticity ofthe propylene units of embodiments of the current invention is the useof triad tacticity. The triad tacticity of a polymer is the relativetacticity of a sequence of three adjacent propylene units, a chainconsisting of head to tail bonds, expressed as a binary combination of mand r sequences. It is usually expressed for copolymers of the presentinvention as the ratio of the number of units of the specified tacticityto all of the propylene triads in the copolymer.

[0060] The triad tacticity (mm fraction) of a propylene copolymer can bedetermined from a ¹³C NMR spectrum of the propylene copolymer and thefollowing formula:${{mm}\quad {Fraction}} = \frac{{PPP}({mm})}{{{PPP}({mm})} + {{PPP}({mr})} + {{PPP}({rr})}}$

[0061] where PPP(mm), PPP(mr) and PPP(rr) denote peak areas derived fromthe methyl groups of the second units in the following three propyleneunit chains consisting of head-to-tail bonds:

[0062] The 13C NMR spectrum of the propylene copolymer is measured asdescribed in U.S. Pat. No. 5,504,172. The spectrum relating to themethyl carbon region (19-23 parts per million (ppm)) can be divided intoa first region (21.2-21.9 ppm), a second region (20.3-21.0 ppm) and athird region (19.5-20.3 ppm). Each peak in the spectrum was assignedwith reference to an article in the journal Polymer, Volume 30 (1989),page 1350.

[0063] In the first region, the methyl group of the second unit in thethree propylene unit chain represented by PPP (mm) resonates.

[0064] In the second region, the methyl group of the second unit in thethree propylene unit chain represented by PPP (mr) resonates, and themethyl group (PPE-methyl group) of a propylene unit whose adjacent unitsare a propylene unit and an ethylene unit resonates (in the vicinity of20.7 ppm).

[0065] In the third region, the methyl group of the second unit in thethree propylene unit chain represented by PPP (rr) resonates, and themethyl group (EPE-methyl group) of a propylene unit whose adjacent unitsare ethylene units resonates (in the vicinity of 19.8 ppm).

[0066] Calculation of the Triad Tacticity and Errors in PropyleneInsertion

[0067] The calculation of the triad tacticity is outlined in thetechniques shown in U.S. Pat. No. 5,504,172. Subtraction of the peakareas for the error in propylene insertions (both 2,1 and 1,3) from peakareas from the total peak areas of the second region and the thirdregion, the peak areas based on the 3 propylene units-chains (PPP(mr)and PPP(rr)) consisting of head-to-tail bonds can be obtained. Thus, thepeak areas of PPP(mm), PPP(mr) and PPP(rr) can be evaluated, and hencethe triad tacticity of the propylene unit chain consisting ofhead-to-tail bonds can be determined.

[0068] The propylene copolymers of embodiments of our invention have atriad tacticity of three propylene units, as measured by 13C NMR, ofgreater than 75%, or greater than 80%, or greater than 82%, or greaterthan 85%, or greater than 90%.

[0069] Stereo- and regio- errors in insertion of propylene: 2,1 and 1,3insertions

[0070] The insertion of propylene can occur to a small extent by either2,1 (tail to tail) or 1,3 insertions (end to end). Examples of 2,1insertion are shown in structures 1 and 2 below.

[0071] A peak of the carbon A and a peak of the carbon A′ appear in thesecond region. A peak of the carbon B and a peak of the carbon B′ appearin the third region, as described above. Among the peaks which appear inthe first to third regions, peaks which are not based on the 3 propyleneunit chain consisting of head-to-tail bonds are peaks based on thePPE-methyl group, the EPE-methyl group, the carbon A, the carbon A′, thecarbon B, and the carbon B′.

[0072] The peak area based on the PPE-methyl group can be evaluated bythe peak area of the PPE-methine group (resonance in the vicinity of30.8 ppm), and the peak area based on the EPE-methyl group can beevaluated by the peak area of the EPE-methine group (resonance in thevicinity of 33.1 ppm). The peak area based on the carbon A can beevaluated by twice as much as the peak area of the methine carbon(resonance in the vicinity of 33.9 ppm) to which the methyl group of thecarbon B is directly bonded; and the peak area based on the carbon A′can be evaluated by the peak area of the adjacent methine carbon(resonance in the vicinity of 33.6 ppm) of the methyl group of thecarbon B′. The peak area based on the carbon B can be evaluated by thepeak area of the adjacent methine carbon (resonance in the vicinity of33.9 ppm); and the peak area based on the carbon B′ can be alsoevaluated by the adjacent methine carbon (resonance in the vicinity of33.6 ppm).

[0073] By subtracting these peak areas from the total peak areas of thesecond region and the third region, the peak areas based on the threepropylene unit chains (PPP(mr) and PPP(rr)) consisting of head-to-tailbonds can be obtained. Thus, the peak areas of PPP(mm), PPP(mr) andPPP(rr) can be evaluated, and the triad tacticity of the propylene unitchain consisting of head-to-tail bonds can be determined.

[0074] The proportion of the 2,1-insertions to all of the propyleneinsertions in a propylene elastomer was calculated by the followingformula with reference to article in the journal Polymer, vol. 30(1989), p.1350.

[0075] Proportion of inversely inserted unit based on 2,1-insertion (%)=$\frac{{0.25\quad I\quad \alpha \quad {\beta \left( {{structure}(i)} \right)}} + {0.5\quad I\quad {{\alpha\beta}\left( {{structure}\quad ({ii})} \right)}}}{{I\quad {\alpha\alpha}} + {I\quad {\alpha\beta}\quad \left( {{{structure}({ii})} + {0.5\quad \left( {{I\quad {\alpha\gamma}}\quad + \quad {I\quad \alpha \quad {\beta \left( {{structure}\quad (i)} \right)}} + {I\quad {\alpha\delta}}} \right)}} \right.}} \times 100$

[0076] Naming of the peaks in the above formula was made in accordancewith a method by Carman, et al. in the journal Rubber Chemistry andTechnology, volume 44 (1971), page 781, where I_(αδ) denotes a peak areaof the αδ⁺ secondary carbon peak. It is difficult to separate the peakarea of Iαβ (structure (i)) from Iαβ (structure (ii)) because ofoverlapping of the peaks. Carbon peaks having the corresponding areascan be substituted therefor.

[0077] The measurement of the 1,3 insertion requires the measurement ofthe βγ peak. Two structures can contribute to the βγ peak: (1) a 1,3insertion of a propylene monomer; and (2) from a 2,1-insertion of apropylene monomer followed by two ethylene monomers. This peak isdescribed as the 1.3 insertion peak and we use the procedure describedin U.S. Pat. No. 5,504,172, which describes this βγ peak and understandit to represent a sequence of four methylene units. The proportion (%)of the amount of these errors was determined by dividing the area of theβγ peak (resonance in the vicinity of 27.4 ppm) by the sum of all themethyl group peaks and {fraction (1/2)} of the area of the βγ peak, andthen multiplying the resulting value by 100. If an α-olefin of three ormore carbon atoms is polymerized using an olefin polymerizationcatalyst, a number of inversely inserted monomer units are present inthe molecules of the resultant olefin polymer. In polyolefins preparedby polymerization of α-olefins of three or more carbon atoms in thepresence of a chiral metallocene catalyst, 2,1-insertion or1,3-insertion takes place in addition to the usual 1,2-insertion, suchthat inversely inserted units such as a 2,1-insertion or a 1,3-insertionare formed in the olefin polymer molecule (see, Macromolecular ChemistryRapid Communication, Volume 8, page 305 (1987), by K. Soga, T. Shiono,S. Takemura and W. Kaminski).

[0078] The proportion of inversely inserted propylene units ofembodiments of our invention, based on the 2,1-insertion of a propylenemonomer in all propylene insertions, as measured by ¹³C NMR, is greaterthan 0.5%, or greater than 0.6%.

[0079] The proportion of inversely inserted propylene units ofembodiments of our invention, based on the 1,3-insertion of a propylenemonomer, as measured by ¹³C NMR, is greater than 0.05%, or greater than0.06%, or greater than 0.07%, or greater than 0.08%, or greater than0.085 percent.

[0080] Molecular Structure

[0081] Homogeneous distribution

[0082] Homogeneous distribution is defined as a statisticallyinsignificant intermolecular difference of both in the composition ofthe copolymer and in the tacticity of the polymerized propylene. For acopolymer to have a homogeneous distribution it must meet therequirement of two independent tests: (i) intermolecular distribution oftacticity; and (ii) intermolecular distribution of composition, whichare described below. These tests are a measure of the statisticallyinsignificant intermolecular differences of tacticity of the polymerizedpropylene and the composition of the copolymer, respectively.

[0083] Intermolecular Distribution of Tacticity

[0084] The copolymer of embodiments of our invention has a statisticallyinsignificant intermolecular difference of tacticity of polymerizedpropylene between different chains (intermolecularly.). This isdetermined by thermal fractionation by controlled dissolution generallyin a single solvent, at a series of slowly elevated temperatures. Atypical solvent is a saturated hydrocarbon such as hexane or heptane.These controlled dissolution procedures are commonly used to separatesimilar polymers of different crystallinity due to differences inisotactic propylene sequences, as shown in the article inMacromolecules, Vol. 26, p2064 (1993). For the copolymers of embodimentsof our invention where the tacticity of the propylene units determinesthe extent of crystallinity, we expected this fractionation procedurewill separate the molecules according to tacticity of the incorporatedpropylene. This procedure is described below.

[0085] In embodiments of our invention, at least 75% by weight, or atleast 80% by weight, or at least 85% by weight, or at least 90% byweight, or at least 95% by weight, or at least 97% by weight, or atleast 99% by weight of the copolymer is soluble in a single temperaturefraction, or in two adjacent temperature fractions, with the balance ofthe copolymer in immediately preceding or succeeding temperaturefractions. These percentages are fractions, for instance in hexane,beginning at 23° C. and the subsequent fractions are in approximately 8°C. increments above 23° C. Meeting such a fractionation requirementmeans that a polymer has statistically insignificant intermoleculardifferences of tacticity of the polymerized propylene.

[0086] Fractionations have been done where boiling pentane, hexane,heptane and even di-ethyl ether are used for the fractionation. In suchboiling solvent fractionations, polymers of embodiments of our inventionwill be totally soluble in each of the solvents, offering no analyticalinformation. For this reason, we have chosen to do the fractionation asreferred to above and as detailed herein, to find a point within thesetraditional fractionations to more fully describe our polymer and thesurprising and unexpected insignificant intermolecular differences oftacticity of the polymerized propylene.

[0087] Intermolecular Distribution of Composition

[0088] The copolymer of embodiments of our invention has statisticallyinsignificant intermolecular differences of composition, which is theratio of propylene to ethylene between different chains(intermolecular). This compositional analysis is by infraredspectroscopy of the fractions of the polymer obtained by the controlledthermal dissolution procedure described above.

[0089] A measure of the statistically insignificant intermoleculardifferences of composition, each of these fractions has a composition(wt. % ethylene content) with a difference of less than 1.5 wt. %(absolute) or less than 1.0 wt. % (absolute), or less than 0.8 wt. %(absolute) of the average wt. % ethylene content of the whole copolymer.Meeting such a fractionation requirement means that a polymer hasstatistically insignificant intermolecular differences of composition,which is the ratio of propylene to ethylene.

[0090] Uniformity

[0091] Uniformity is defined to be a statistically insignificantintramolecular difference of both the composition of the copolymer andin the tacticity of the polymerized propylene. For a copolymer to beuniform it must meet the requirement of two independent tests: (i)intramolecular distribution of tacticity; and (ii) intramoleculardistribution of composition, which are described below. These tests area measure of the statistically insignificant intramolecular differencesof tacticity of the polymerized propylene and the composition of thecopolymer, respectively.

[0092] Intramolecular Distribution of Composition

[0093] The copolymer of embodiments of our invention has statisticallyinsignificant intramolecular differences of composition, which is theratio of propylene to ethylene along the segments of the same chain(intramolecular). This compositional analysis is inferred from theprocess used for the synthesis of these copolymers as well as theresults of the sequence distribution analysis of the copolymer, formolecular weights in the range of from 15,000-5,000,000 or20,000-1,000,000.

[0094] Process

[0095] The polymerization process is a single stage, steady state,polymerization conducted in a well-mixed continuous feed polymerizationreactor. The polymerization can be conducted in solution, although otherpolymerization procedures such as gas phase or slurry polymerization,which fulfil the requirements of single stage polymerization andcontinuous feed reactors, are contemplated.

[0096] The process can be described as a continuous, non-batch processthat, in its steady state operation, is exemplified by removal ofamounts of polymer made per unit time, being substantially equal to theamount of polymer withdrawn from the reaction vessel per unit time. By“substantially equal” we intend that these amounts, polymer made perunit time, and polymer withdrawn per unit time, are in ratios of one toother, of from 0.9:1; or 0.95:1; or 0.97:1; or 1:1. In such a reactor,there will be a substantially homogeneous monomer distribution. At thesame time, the polymerization is accomplished in substantially singlestep or stage or in a single reactor, contrasted to multistage ormultiple reactors (two or more). These conditions exist forsubstantially all of the time the copolymer is produced.

[0097] Monomer Sequence Distribution

[0098] One method to describe the molecular features of anethylene-propylene copolymer is monomer sequence distribution. Startingwith a polymer having a known average composition, the monomer sequencedistribution can be determined using spectroscopic analysis. Carbon 13nuclear magnetic resonance spectroscopy (¹³C NMR) can be used for thispurpose, and can be used to establish diad and triad distribution viathe integration of spectral peaks. (If ¹³C NMR is not used for thisanalysis, substantially lower r₁r₂ products are normally obtained.) Thereactivity ratio product is described more fully in Textbook of PolymerChemistry, F. W. Billmeyer, Jr., Interscience Publishers, New York,p.221 et seq. (1957).

[0099] The reactivity ratio product r₁r₂, where r₁ is the reactivity ofethylene and r₂ is the reactivity of propylene, can be calculated fromthe measured diad distribution (PP, EE, EP and PE in this nomenclature)by the application of the following formulae:

r ₁ r ₂=4(EE)(PP)/(EP)²

r ₁ =K ₁₁ /K ₁₂=[2(EE)/EP]X

r ₂ =K ₂₂ /K ₂₁=[2(PP)/(EP)]X

P=(PP)+(EP/2)

E=(EE)+(EP/2)

[0100] where

[0101] Mol % E=[(E)/(E+P)]*100

[0102] X=E/P in reactor;

[0103] K₁₁ and K₁₂ are kinetic insertion constants for ethylene; and

[0104] K₂₁ and K₂₂ are kinetic insertion constants for propylene.

[0105] As is known to those skilled in the art, a reactivity ratioproduct r₁r₂ of 0 can define an “alternating” copolymer, and areactivity ratio product of 1 is said to define a “statistically random”copolymer. In other words, a copolymer having a reactivity ratio productr₁r₂ of between 0.6 and 1.5 is generally said to be random (in stricttheoretical terms, generally only a copolymer having a reactivity ratioproduct r₁r₂ greater than 1.5 contains relatively long homopolymersequences and is said to be “blocky”). The copolymer of our inventionwill have a reactivity ratio product r₁r₂ of less than 1.5, or less than1.3, or less than 1.0, or less than 0.8. The substantially uniformdistribution of comonomer within polymer chains of embodiments of ourinvention generally precludes the possibility of significant amounts ofpropylene units or sequences within the polymer chain for the molecularweights (weight average) disclosed herein.

[0106] Intramolecular distribution of tacticity

[0107] The copolymer of embodiments of our invention has statisticallyinsignificant intramolecular differences of tacticity, which is due toisotactic orientation of the propylene units along the segments of thesame chain (intramolecular). This compositional analysis is inferredfrom the detailed analysis of the differential scanning calorimetry,electron microscopy and relaxation measurement (T_(1p)). In the presenceof significant intramolecular differences in tacticity, we would form‘stereoblock’ structures, where the number of isotactic propyleneresidues adjacent to one another is much greater than statistical.Further, the melting point of these polymers depends on thecrystallinity, since the more blocky polymers should have a highermelting point as well as depressed solubility in room temperaturesolvents.

[0108] T_(1p): Solid-state ¹H NMR T_(1p) relaxation time

[0109] The principle of solid state proton NMR relaxation time (¹H NMRT_(1p)) and its relationship with polymer morphology have been discussedin Macromolecules 32 (1999), 1611. The experimental T_(1p) relaxationdata of embodiments of the current invention, and polypropylene (PP)homopolymer (control sample) are shown in FIG. 1, which plots thenatural log of the crystalline intensity versus time; the experimentalprocedure for collecting these data is described below. To fit the datawith single exponential function, linear regression was performed on theln(I) vs. t data, where I is the intensity of the crystalline signal.Then, the quality of the fit, R², is calculated. The R² for a perfectlinear correlation is 1.0. The R² for polypropylene (control) and acopolymer of the current invention (shown in FIG. 1) are 0.9945 and0.9967, respectively. Therefore, the T_(1p) relaxation for bothpolypropylene homopolymer and a copolymer of the current invention canbe well fitted by a single-exponential. From the fit, the T_(1p) ofpolypropylene and a copolymer of the present invention, are calculatedas 25 milliseconds (ms) and 8.7 ms, respectively. The large differencein the T_(1p) is reflective of their difference in morphology.

[0110] The hypothetical polypropylene-like regions would have T_(1p)relaxation similar to that in polypropylene homopolymer. As a result,should such regions exist in embodiments of the invention, the T_(1p)relaxation would contain a component that has a T_(1p) relaxation timecharacteristic of polypropylene homopolymer (i.e., T_(1p)=25 ms). Asseen in FIG. 1, the T_(1p) relaxation of the current invention can onlybe well fitted by a single exponential. Incorporation of a componentwhose T_(1p)=25 ms would deteriorate the fit. This demonstrates that thepolymers of the current invention do not contain long continuousisotactic propylene units. In embodiments of our invention, the T_(1p),relaxation time can be less than 18 ms, or less than 16 ms, or less than14 ms, or less than 12 ms, or less than 10 ms.

[0111] T_(1p) Measurement.

[0112] The experiments are performed on a Bruker DSX-500 NuclearMagnetic Resonance (NMR) spectrometer, with a ¹H frequency of 500.13 MHzand ¹³C frequency of 125.75 MHz. The pulse sequence was a 90° (¹H) pulsefollowed by spin lock and cross polarization (“CP”; time=0.1 ms). A spinlock field strength of γB₁=2π*60 kHz is used. After the spin lock, themagnetization is transferred to ¹³C by CP and then the signal isdetected. The crystalline methine signal at 26.7 ppm is recorded andnormalized and its natural logarithm (Ln) is plotted against spin locktime in FIG. 1. Measurements were made on a polypropylene homopolymersample, and on a polymer of the present invention, labeled “Sample 4”and described in the Examples below. Table 1 presents the data. TABLE 1Time (ms) Ln(I) (sample 4) Ln(I) (PP) 0.02 0 0 0.5 −0.11394 −0.02496 1−0.18772 −0.04733 2 −0.32424 −0.09871 5 −0.71649 −0.24692 10 −1.27022−0.44715 20 −2.34181 −0.79526

[0113] Catalysts and Activators for Copolymer Production Catalysts

[0114] A typical isotactic polymerization process consists of apolymerization in the presence of a catalyst including abis(cyclopentadienyl) metal compound and either (1) a non-coordinatingcompatible anion activator, or (2) an alumoxane activator. According toone embodiment of the invention, this process comprises the steps ofcontacting ethylene and propylene with a catalyst in a suitablepolymerization diluent, the catalyst including, in one embodiment, achiral metallocene compound, e.g., a bis(cyclopentadienyl) metalcompound as described in U.S. Pat. No. 5,198,401, and an activator. U.S.Pat. No. 5,391,629 also describes catalysts useful to produce thecopolymers of our invention.

[0115] The catalyst system described below useful for making thecopolymers of embodiments of our invention, is a metallocene with anon-coordinating anion (NCA) activator, and optionally a scavengingcompound. Polymerization is conducted in a solution, slurry or gasphase. The polymerization can be performed in a single reactor process.A slurry or solution polymerization process can utilize sub- orsuperatmospheric pressures and temperatures in the range of from −25° C.to 110° C. In a slurry polymerization, a suspension of solid,particulate polymer is formed in a liquid polymerization medium to whichethylene, propylene, hydrogen and catalyst are added. In solutionpolymerization, the liquid medium serves as a solvent for the polymer.The liquid employed as the polymerization medium can be an alkane or acycloalkane, such as butane, pentane, hexane, or cylclohexane, or anaromatic hydrocarbon, such as toluene, ethylbenzene or xylene. Forslurry polymerization, liquid monomer can also be used. The mediumemployed should be liquid under the conditions of the polymerization andrelatively inert. Hexane or toluene can be employed for solutionpolymerization. Gas phase polymerization processes are described in U.S.Pat. Nos. 4,543,399, 4,588,790, 5,028,670, for example. The catalyst canbe supported on any suitable particulate material or porous carrier,such as polymeric supports or inorganic oxides, such as, for examplesilica, alumina or both. Methods of supporting metallocene catalysts aredescribed in U.S. Pat. Nos. 4,808,561, 4,897,455, 4,937,301, 4,937,217,4,912,075, 5,008,228, 5,086,025, 5,147,949, and 5,238,892.

[0116] Propylene and ethylene are the monomers that can be used to makethe copolymers of embodiments of our invention, but optionally, ethylenecan be replaced or added to in such polymers with a C4 to C20 α-olefin,such as, for example, 1-butene, 4-methyl-1-pentene, 1-hexene or1-octene.

[0117] Metallocene

[0118] The terms “metallocene” and “metallocene catalyst precursor” areterms known in the art to mean compounds possessing a Group 4, 5, or 6transition metal M, with a cyclopentadienyl (Cp) ligand or ligands whichmay be substituted, at least one non-cyclopentadienyl-derived ligand X,and zero or one heteroatom-containing ligand Y, the ligands beingcoordinated to M and corresponding in number to the valence thereof. Themetallocene catalyst precursors generally require activation with asuitable co-catalyst (sometimes referred to as an activator) in order toyield an active metallocene catalyst, i.e., an organometallic complexwith a vacant coordination site that can coordinate, insert, andpolymerize olefins.

[0119] Preferred metallocenes are cyclopentadienyl complexes which havetwo Cp ring systems as ligands. The Cp ligands preferably form a bentsandwich complex with the metal, and are preferably locked into a rigidconfiguration through a bridging group. These cyclopentadienyl complexeshave the general formula:

(Cp ¹ R ¹ m)R ³ n(Cp ² R ² p)MX _(q)

[0120] wherein Cp¹ and Cp² are preferably the same; R¹ and R² are each,independently, a halogen or a hydrocarbyl, halocarbyl,hydrocarbyl-substituted organometalloid or halocarbyl-substitutedorganometalloid group containing up to 20 carbon atoms; m is preferably1 to 5; p is preferably 1 to 5; preferably two R¹ and/or R² substituentson adjacent carbon atoms of the cyclopentadienyl ring associatedtherewith can be joined together to form a ring containing from 4 to 20carbon atoms; R³ is a bridging group; n is the number of atoms in thedirect chain between the two ligands and is preferably 1 to 8, mostpreferably 1 to 3; M is a transition metal having a valence of from 3 to6, preferably from group 4, 5, or 6 of the periodic table of theelements, and is preferably in its highest oxidation state; each X is anon-cyclopentadienyl ligand and is, independently, a hydrocarbyl,oxyhydrocarbyl, halocarbyl, hydrocarbyl-substituted organometalloid,oxyhydrocarbyl-substituted organometalloid or halocarbyl-substitutedorganometalloid group containing up to 20 carbon atoms; and q is equalto the valence of M minus 2.

[0121] Numerous examples of the biscyclopentadienyl metallocenesdescribed above for the invention are disclosed in U.S. Pat. Nos.5,324,800; 5,198,401; 5,278,119; 5,387,568; 5,120,867; 5,017,714;4,871,705; 4,542,199; 4,752,597; 5,132,262; 5,391,629; 5,243,001;5,278,264; 5,296,434; and 5,304,614.

[0122] Illustrative, but not limiting examples of preferredbiscyclopentadienyl metallocenes of the type described above are theracemic isomers of:

[0123] μ-(CH₃)₂Si(indenyl)₂M(Cl)₂,

[0124] μ-(CH₃)₂Si(indenyl)₂M(CH₃)₂,

[0125] μ-(CH₃)₂Si(tetrahydroindenyl)₂M(Cl)₂,

[0126] μ-(CH₃)₂Si(tetrahydroindenyl)₂M(CH₃)₂,

[0127] μ-(CH₃)₂Si(indenyl)₂M(CH₂CH₃)₂, and

[0128] μ-(C₆H₅)₂C(indenyl)₂M(CH₃)₂,

[0129] wherein M is Zr, Hf, or Ti.

[0130] Non-coordinating anions

[0131] As already mentioned, the metallocene or precursor are activatedwith a non-coordinating anion. The term “non-coordinating anion” meansan anion which either does not coordinate to the transition metal cationor which is only weakly coordinated to the cation, thereby remainingsufficiently labile to be displaced by a neutral Lewis base.“Compatible” non-coordinating anions are those which are not degraded toneutrality when the initially formed complex decomposes. Further, theanion will not transfer an anionic substituent or fragment to the cationso as to cause it to form a neutral four coordinate metallocene compoundand a neutral by-product from the anion. Non-coordinating anions usefulin accordance with this invention are those which are compatible,stabilize the metallocene cation in the sense of balancing its ioniccharge, yet retain sufficient lability to permit displacement by anethylenically or acetylenically unsaturated monomer duringpolymerization. Additionally, the anions useful in this invention may belarge or bulky in the sense of sufficient molecular size to largelyinhibit or prevent neutralization of the metallocene cation by Lewisbases other than the polymerizable monomers that may be present in thepolymerization process. Typically the anion will have a molecular sizeof greater than or equal to 4 angstroms.

[0132] Descriptions of ionic catalysts for coordination polymerizationincluding metallocene cations activated by non-coordinating anionsappear in the early work in EP-A-0 277 003, EP-A-0 277 004, U.S. Pat.Nos. 5,198,401 and 5,278,119, and WO 92/00333. These references suggesta method of preparation wherein metallocenes (bis Cp and mono Cp) areprotonated by anionic precursors such that an alkyl/hydride group isabstracted from a transition metal to make it both cationic andcharge-balanced by the non-coordinating anion. The use of ionizing ioniccompounds not containing an active proton but capable of producing boththe active metallocene cation and a non-coordinating anion is alsoknown. See, EP-A-0 426 637, EP-A-0 573 403 and U.S. Pat. No. 5,387,568.Reactive cations other than Bronsted acids capable of ionizing themetallocene compounds include ferrocenium, triphenylcarbonium, andtriethylsilylium cations. Any metal or metalloid capable of forming acoordination complex which is resistant to degradation by water (orother Bronsted or Lewis acids) may be used or contained in the anion ofthe second activator compound. Suitable metals include, but are notlimited to, aluminum, gold, platinum and the like. Suitable metalloidsinclude, but are not limited to, boron, phosphorus, silicon and thelike.

[0133] An additional method of making the ionic catalysts uses ionizinganionic pre-cursors which are initially neutral Lewis acids but form thecation and anion upon ionizing reaction with the metallocene compounds.For example tris(pentafluorophenyl) boron acts to abstract an alkyl,hydride or silyl ligand to yield a metallocene cation and stabilizingnon-coordinating anion; see EP-A-0 427 697 and EP-A-0 520 732. Ioniccatalysts for addition polymerization can also be prepared by oxidationof the metal centers of transition metal compounds by anionic precursorscontaining metallic oxidizing groups along with the anion groups; seeEP-A-0 495 375.

[0134] Illustrative, but not limiting, examples of suitable activatorscapable of ionic cationization of the metallocene compounds of theinvention, and consequent stabilization with a resultingnon-coordinating anion, include:

[0135] trialkyl-substituted ammonium salts such as:

[0136] triethylammonium tetraphenylborate;

[0137] tripropylammonium tetraphenylborate;

[0138] tri(n-butyl)ammonium tetraphenylborate;

[0139] trimethylammonium tetrakis(p-tolyl)borate;

[0140] trimethylammonium tetrakis(o-tolyl)borate;

[0141] tributylammonium tetrakis(pentafluorophenyl)borate;

[0142] tripropylammonium tetrakis(o,p-dimethylphenyl)borate;

[0143] tributylammonium tetrakis(m,m-dimethylphenyl)borate;

[0144] tributylammonium tetrakis(p-trifluoromethylphenyl)borate;

[0145] tributylammonium tetrakis(pentafluorophenyl)borate;

[0146] tri(n-butyl)ammonium tetrakis(o-tolyl)borate and the like;

[0147] N,N-dialkyl anilinium salts such as:

[0148] N,N-dimethylanilinium tetrakis(pentafluorophenyl)borate;

[0149] N,N-dimethylanilinium tetrakis(heptafluoronaphthyl)borate;

[0150] N,N-dimethylanilinium tetrakis(perfluoro-4-biphenyl)borate;

[0151] N,N-dimethylanilinium tetraphenylborate;

[0152] N,N-diethylanilinium tetraphenylborate;

[0153] N,N-2,4,6-pentamethylanilinium tetraphenylborate and the like;

[0154] dialkyl ammonium salts such as:

[0155] di-(isopropyl)ammonium tetrakis(pentafluorophenyl)borate;

[0156] dicyclohexylammonium tetraphenylborate and the like; and

[0157] triaryl phosphonium salts such as:

[0158] triphenylphosphonium tetraphenylborate;

[0159] tri(methylphenyl)phosphonium tetraphenylborate;

[0160] tri(dimethylphenyl)phosphonium tetraphenylborate and the like.

[0161] Further examples of suitable anionic precursors include thosecomprising a stable carbonium ion, and a compatible non-coordinatinganion. These include:

[0162] tropyllium tetrakis(pentafluorophenyl)borate;

[0163] triphenylmethylium tetrakis(pentafluorophenyl)borate;

[0164] benzene (diazonium) tetrakis(pentafluorophenyl)borate;

[0165] tropyllium phenyltris(pentafluorophenyl)borate;

[0166] triphenylmethylium phenyl-(trispentafluorophenyl)borate;

[0167] benzene (diazonium) phenyltris(pentafluorophenyl)borate;

[0168] tropyllium tetrakis(2,3,5,6-tetrafluorophenyl)borate;

[0169] triphenylmethylium tetrakis(2,3,5,6-tetrafluorophenyl)borate;

[0170] benzene (diazonium) tetrakis(3,4,5tetrafluorophenyl)borate;

[0171] tropyllium tetrakis(3,4,5-trifluorophenyl)borate;

[0172] benzene (diazonium) tetrakis(3,4,5-trifluorophenyl)borate;

[0173] tropyllium tetrakis(3,4,5-trifluorophenyl)aluminate;

[0174] triphenylmethylium tetrakis(3,4,5-trifluorophenyl)aluminate;

[0175] benzene (diazonium) tetrakis(3,4,5-trifluorophenyl)aluminate;

[0176] tropyllium tetrakis(1,2,2-trifluoroethenyl)borate;

[0177] triphenylmethylium tetrakis(1,2,2-trifluoroethenyl)borate;

[0178] benzene (diazonium) tetrakis(1,2,2-trifluoroethenyl)borate;

[0179] tropyllium tetrakis(2,3,4,5-tetrafluorophenyl)borate;

[0180] triphenylmethylium tetrakis(2,3,4,5-tetrafluorophenyl)borate;

[0181] benzene (diazonium) tetrakis(2,3,4,5-tetrafluorophenyl)borate,and the like.

[0182] A catalyst system of μ-(CH₃)₂Si(indenyl)₂Hf(CH₃)₂ with acocatalyst of N,N-dimethylanilinium tetrakis(pentafluorophenyl)borate,can be used.

[0183] Properties and Analysis of the Copolymer Elongation and TensileStrength

[0184] Elongation and tensile strength were measured as described below.The copolymers of the current invention have an elongation of greaterthan 1000%, or greater than 1200%, or greater than 1500%.

[0185] The copolymers of the current invention have a tensile strengthgreater than 300 psi (2.1 MPa), or greater than 500 psi (3.5 MPa) orgreater than 1000 psi (6.9 MPa).

[0186] Tensile and elongation properties are determined at 20 in/min (51cm/min) according to the procedure described in ASTM D790. The data isreported in engineering units with no correction to the stress for thelateral contraction in the specimen due to tensile elongation. Thetensile and elongation properties of embodiments of our invention areevaluated using dumbbell-shaped samples. The samples are compressionmolded at 180° C. to 200° C. for 15 minutes at a force of 15 tons (133kN) into a plaque of dimensions of 6 in×6 in (15 cm×15 cm). The cooledplaques are removed and the specimens are removed with a die. Theelasticity evaluation of the samples is conducted on an Instron 4465,made by Instron Corporation of 100 Royall Street, Canton, Mass. Thedigital data is collected in a file collected by the Series IX MaterialTesting System available from Instron Corporation and analyzed usingExcel 5, a spreadsheet program available from Microsoft Corporation ofRedmond, Wash.

[0187] Elasticity

[0188] Embodiments of our invention are elastic after tensiledeformation. The elasticity, represented by the fractional increase inthe length of the sample, represented as percent of the length of thesample, is measured according to the general procedure ASTM D790. Duringtensile elongation, the copolymer sample is stretched, and the polymerattempts to recover its original dimensions when the stretching force isremoved. This recovery is not complete, and the final length of therelaxed sample is slightly longer than that of the original sample.Elasticity is represented by the fractional increase in the length ofthe sample, expressed as a percent of the length of the originalun-stretched sample.

[0189] The protocol for measuring the elasticity of the sample consistsof prestretching the deformable zone of the dumbbell, made according tothe procedure described above for the measurement of elongation andtensile strength, which is the narrow portion of the specimen, to 200%of its original length to prestretch the sample. This is conducted at adeformation rate of 10 inches (25 cm) per minute. The sample is relaxedat the same rate to form an analytical specimen which is a prestretchedspecimen of the original sample. This slightly oriented, orprestretched, sample is allowed to relax for 48 hours, at roomtemperature, prior to the determination of elasticity. The length of thedeformation zone in the sample is measured to be d₁. After the 48 hours,it is again deformed at 10 inches per minute for a 200% extension of thedeformation zone of the sample and allowed to relax at the same rate.The sample is removed and after 10 minutes of relaxation the sample ismeasured to have a new length of the deformation zone of d₂. Theelasticity of the sample as a percent is determined as 100*(d₂-d₁)/d₁.

[0190] Embodiments of the invention have elasticity, as measured by theprocedure described above, of less than 30%, or less than 20%, or lessthan 10%, or less than 8% or less than 5%.

[0191] These values of the elasticity over the range of composition ofthe copolymer vary with the tensile strength of the sample as measuredby the 500% tensile modulus. Elasticity of this family of copolymers isthus represented by two criteria: (a) extensibility to 500% elongationwith a measurable modulus (500% tensile modulus) and (b) elasticity froman extension to 200% elongation on a slightly oriented sample asdescribed above. First, the copolymer of embodiments of our inventionshould have a measurable tensile strength at 500% elongation (also knownas 500% tensile modulus), of greater than 0.5 MPa, or greater than 0.75MPa, or greater than 1.0 MPa, or greater than 2.0 MPa; and second, thecopolymer should have the above-described elasticity.

[0192] Alternatively, the relationship of elasticity to 500% tensilemodulus may be described. Referring to FIG. 3, elasticity is plottedversus 500% tensile modulus in MPa for copolymers of the invention. Theplotted data correspond to Samples 5-14 in Table 6 of the Examplesherein. A linear regression fit of the data yields a relationship of:

Elasticity (%)=0.9348M−1.0625

[0193] where M is the 500% tensile modulus in MPa. In embodiments of thepresent invention, the elasticity as a function of 500% tensile modulusin MPa is defined by:

Elasticity (%)≦0.935M+12; or

Elasticity (%)≦0.935M+6; or

Elasticity (%)≦0.935M.

[0194] Flexural Modulus

[0195] Softness of the copolymers of embodiments of the invention may bemeasured by flexural modulus. Flexural modulus is measured in accordancewith ASTM D790, using a Type IV dogbone at crosshead speed of 0.05in/min (1.3 mm/min). The values of the flexural modulus over the rangeof composition of the copolymer vary with the tensile strength of thesample as measured by the 500% tensile modulus. Flexural modulus of thisfamily of copolymers is thus represented by two criteria: (a)extensibility to 500% elongation with a measurable modulus (500% tensilemodulus); and (b) flexural modulus.

[0196] Referring to FIG. 2, flexural modulus in MPa is plotted versus500% tensile modulus in MPa for copolymers of the invention. The plotteddata correspond to Samples 15-19 in Table 7 of the Examples herein. Asingle exponential fit of the data yields a relationship of:

Flexural Modulus (MPa)=4.1864e ^(0.269M)

[0197] where M is the 500% tensile modulus in MPa. In embodiments of thepresent invention, the flexural modulus in MPa as a function of 500%tensile modulus in MPa is defined by:

Flexural Modulus≦4.2e ^(0.27M)+50; or

Flexural Modulus≦4.2e ^(0.27M)+30; or

Flexural Modulus≦4.2e ^(0.27M)+10; or

Flexural Modulus≦4.2e ^(0.27M)+2.

[0198] Ethylene Composition

[0199] The composition of ethylene propylene copolymers is measured asethylene wt. % according to ASTM D3900 as follows. A thin homogeneousfilm of the copolymer component, pressed at a temperature of at orgreater than 150° C., is mounted on a Perkin Elmer PE 1760 infra redspectrophotometer. A full spectrum of the sample from 600 cm⁻¹ to 4000cm⁻¹ is recorded, and the ethylene weight percent of the copolymercomponent is calculated from:

Ethylene wt. %=82.585-111.987X+30.045X ²

[0200] where X is the ratio of the peak height at 1155 cm⁻¹ to peakheight at either 722 cm⁻¹ or 732 cm⁻¹, which ever is higher.

[0201] Molecular Weight and PDI

[0202] Techniques for determining the molecular weight (Mn and Mw) andmolecular weight distribution (MWD) are found in U.S. Pat. No.4,540,753, and in Macromolecules, 1988, volume 21, p. 3360 (Verstrate etal).

[0203] Melting Point and Heat of Fusion

[0204] Melting point and heat of fusion are measured by DifferentialScanning Calorimetry (DSC) follows. About 6 to 10 mg of a sheet of thepolymer pressed at approximately 200° C. to 230° C. is removed with apunch die. This is annealed at room temperature for 24 hours. At the endof this period, the sample is placed in a Differential ScanningCalorimeter (Perkin Elmer 7 Series Thermal Analysis System) and cooledto about −50° C. to about −70° C. The sample is heated at 20° C./min toattain a final temperature of about 200° C. to about 220° C. The thermaloutput is recorded as the area under the melting peak of the sample,which is typically peaked at about 30° C. to about 175° C. and occursbetween the temperatures of about 0° C. and about 200° C., and ismeasured in joules as a measure of the heat of fusion. The melting pointis recorded as the temperature of the greatest heat absorption withinthe range of melting of the sample.

[0205] Intermolecular Composition and Tacticity DistributionDetermination

[0206] Intermolecular composition distribution of the copolymer ismeasured as described below. Nominally 30 grams of the copolymer is cutinto small cubes with about {fraction (1/8)}″ (3 mm) sides. This isintroduced into a thick-walled glass bottle with a screw cap closure,along with 50 mg of Irganox1076, an antioxidant commercially availablefrom Ciba-Geigy Corporation. Then, 425 mL of hexane (a principal mixtureof normal and iso isomers) is added to the bottle and the sealed bottleis maintained at 23° C. for 24 hours. At the end of this period, thesolution is decanted and the residue is treated with additional hexanefor an additional 24 hours. At the end of this period, the two hexanesolutions are combined and evaporated to yield a residue of the polymersoluble at 23° C. To the residue is added sufficient hexane to bring thevolume to 425 mL and the bottle is maintained at 31° C. for 24 hours ina covered circulating water bath. The soluble polymer is decanted and anadditional amount of hexane is added for another 24 hours at 31° C.prior to decanting. In this manner, fractions of the copolymers solubleat 40° C., 48° C., 55° C. and 62° C. are obtained at temperatureincreases of approximately 8° C. between stages. Increases intemperature to 95° C. can be accommodated if heptane, instead of hexane,is used as the solvent for all temperatures above about 60° C. Thesoluble polymers are dried, weighed and analyzed for composition, as wt.% ethylene content, by the IR technique described above. Solublefractions obtained in the adjacent temperature fractions are theadjacent fractions in the specification above.

EXAMPLES Example 1

[0207] Ethylene/propylene copolymerization

[0208] Continuous polymerization of the polymer is conducted in a 9liter Continuous Flow Stirred Tank Reactor using hexane as the solvent.The liquid full reactor has a residence time of 9 minutes and thepressure is maintained at 700 kPa. A mixed feed of hexane, ethylene andpropylene is pre-chilled to approximately −30° C. to remove the heat ofpolymerization, before entering the reactor. Solutions ofcatalyst/activator in toluene and the scavenger in hexane are separatelyand continuously admitted into the reactor to initiate thepolymerization. The reactor temperature is maintained between 35 and 50°C., depending on the target molecular weight. The feed temperature isvaried, depending on the polymerization rate to maintain a constantreactor temperature. The polymerization rate is varied from about 0.5kg/hr to about 4 kg/hr. Hexane at 30 kg/hr is mixed with ethylene at 717g/hr and propylene at 5.14 kg/hr and fed to the reactor. Thepolymerization catalyst, dimethylsilyl bridged bis-indenyl hafniumdimethyl activated 1.1 molar ratio with N′,N′-dimethylanilinium-tetrakis (pentafluorophenyl)borate is introduced at the rateof at 0.0135 g/hr. A dilute solution of triisobutyl aluminum isintroduced into the reactor as a scavenger of catalyst terminators; arate of approximately 111 mol of scavenger per mole of catalyst isadequate for this polymerization After the polymerization reaches steadystate, a representative sample of the polymer produced in thispolymerization is collected, and then steam-distilled to isolate thepolymer. The polymerization rate is measured as 3.7 kg/hr. The polymerproduced in this polymerization has an ethylene content of 14%, ML (1+4)125° C. (Mooney Viscosity) of 13.1 and has isotactic propylenesequences.

[0209] Variations in the composition of the polymer are obtainedprincipally by changing the ratio of ethylene to propylene. Molecularweight of the polymer is varied by either changing the reactortemperature or by changing the ratio of total monomer feed rate to thepolymerization rate.

[0210] In the manner described in Example 1 above, polymers of the abovespecification are synthesized. These are described in the tables below.Table 2 describes the results of the GPC, composition, and DSC analysisfor the polymers. TABLE 2 Analysis of the polymers ¹³C NMR RESULTS DSCResults Ethylene Triad 2,1 insertion 1,3 insertion Heat of MeltingSample # (wt %) (mm) (%) (%) m/r fusion (J/g) Point (° C.) #1 11.0 90.10.63 0.098 7.1 19 49 #2 18.5 91.3 0.84 0.12  6.2 1.8 50 #3 9.4 91.8 0.800.086 6.9 27 69 #4 14.1 90.6 0.74 0.13  7.7 8.0 51

[0211] TABLE 3 Fractional solubility of copolymer (hexane) Wt % solubleat T Sample # 23° C. 31° C. 40° C. 1 39.2 60.0 0.5 2 97.6 2.1 3 0.7 52.348.1 4 99.3 0.7

[0212] Table 4 describes the composition of the fractions of thecopolymer obtained in Table 3. Only fractions which have more than 4% ofthe total mass of the polymer have been analyzed for composition. TABLE4 Composition of fractions of the copolymer component obtained in TABLE3 Composition (wt % C2) for fraction soluble at T Sample # 23° C. 31° C.40° C. 1 10.8 11.3 — 2 17.9 — 3 —  9.9 10.2 4 14.5 —

[0213] The experimental inaccuracy in the determination of the ethylenecontent is believed to be approximately 0.4 wt % absolute. TABLE 5Mechanical properties of the polymers Mechanical Properties TensileStrength 500% Tensile Modulus Sample # (psi, MPa) (psi, MPa) Elasticity(%) 1 3226.5, 22.25 1412, 9.74 17 2 334.0, 2.30 129, 0.889 1.5 3 5041.3,34.76 2300, 15.86 24 4 1277.7, 8.810 387, 2.67 0

[0214] TABLE 6 Composition Mechanical Properties Ethylene Content 500%Tensile Elasticity Sample # (wt %) Modulus (MPa) (%) 5 12.4 6.8 3.1 612.0 7.9 1.6 7 17.0 0.9 1.6 8 11.1 9.9 18.8 9 10.8 8.9 6.4 10 12.1 6.93.1 11 13.4 6.4 1.6 12 14.8 2.7 0 13 16.4 0.6 3.1 14 13.4 7.1 4.7

[0215] TABLE 7 Composition Mechanical Properties Ethylene Content 500%Tensile Flexural Sample # (wt %) Modulus (MPa) Modulus (MPa) 15 12.0 7.926.8 16 14.8 2.7 9.2 17 17.0 0.9 5.6 18 10.8 8.9 40.1 19 10.0 10.3  93.0

[0216] Although the present invention has been described in considerabledetail with reference to certain aspects and embodiments thereof, otheraspects and embodiments are possible. For example, while ethylenepropylene copolymers have been exemplified, other copolymers are alsocontemplated. Therefore, the spirit and scope of the appended claimsshould not be limited to the description of the versions containedherein.

[0217] Certain features of the present invention are described in termsof a set of numerical upper limits and a set of numerical lower limits.It should be appreciated that ranges from any lower limit to any upperlimit are within the scope of the invention unless otherwise indicated.

[0218] All patents, test procedures, and other documents cited in thisapplication are fully incorporated by reference to the extent suchdisclosure is not inconsistent with this application and for alljurisdictions in which such incorporation is permitted.

What is claimed is:
 1. A copolymer comprising 5 to 25% by weight ofethylene-derived units and 95 to 75% by weight of propylene-derivedunits, the copolymer having: (a) a melting point of less than 90° C.;(b) a relationship of elasticity to 500% tensile modulus such thatElasticity ≦0.935M+12,  where elasticity is in percent and M is the 500%tensile modulus in MPa; and (c) a relationship of flexural modulus to500% tensile modulus such that Flexural Modulus ≦4.2e ^(0.27M)+50, where flexural modulus is in MPa and M is the 500% tensile modulus inMPa.
 2. The copolymer of claim 1, wherein the copolymer comprises 6 to20% by weight of ethylene-derived units and 94 to 80% by weight ofpropylene-derived units.
 3. The copolymer of claim 1, wherein thecopolymer comprises 8 to 20% by weight of ethylene-derived units and 92to 80% by weight of propylene-derived units.
 4. The copolymer of claim1, wherein the copolymer comprises 10 to 20% by weight ofethylene-derived units and 90 to 80% by weight of propylene-derivedunits.
 5. The copolymer of claim 1, wherein the melting point is between25 and 90° C.
 6. The copolymer of claim 1, wherein the melting point isbetween 35 and 80° C.
 7. The copolymer of claim 1, wherein the meltingpoint is between 45 and 70° C.
 8. The copolymer of claim 1, wherein therelationship of elasticity to 500% tensile modulus is: Elasticity≦0.935M+6.
 9. The copolymer of claim 1, wherein the relationship ofelasticity to 500% tensile modulus is: Elasticity ≦0.935M.
 10. Thecopolymer of claim 1, wherein the relationship of flexural modulus to500% tensile modulus is: Flexural Modulus ≦4.2e ^(0.27M)+30.
 11. Thecopolymer of claim 1, wherein the relationship of flexural modulus to500% tensile modulus is: Flexural Modulus ≦4.2e ^(0.27M)+10.
 12. Thecopolymer of claim 1, wherein the relationship of flexural modulus to500% tensile modulus is: Flexural Modulus ≦4.2e ^(0.27M)+2.
 13. Thecopolymer of claim 1, wherein the copolymer has a heat of fusion of from1.0 J/g to 40 J/g.
 14. The copolymer of claim 1, wherein the copolymerhas a heat of fusion of from 1.5 J/g to 30 J/g.
 15. The copolymer ofclaim 1, wherein the copolymer has a triad tacticity as determined by¹³C NMR of greater than 75%.
 16. The copolymer of claim 1, wherein thecopolymer has a triad tacticity as determined by ¹³C NMR of greater than85%.
 17. The copolymer of claim 1, wherein the copolymer has a triadtacticity as determined by ¹³C NMR of greater than 90%.
 18. Thecopolymer of claim 1, wherein the copolymer has a tacticity index m/r offrom 4 to
 12. 19. The copolymer of claim 1, wherein the copolymer has atacticity index m/r of from 6 to
 10. 20. The copolymer of claim 1,wherein the copolymer has a proportion of inversely inserted propyleneunits based on 2,1 insertion of propylene monomer in all propyleneinsertions, as measured by ¹³C NMR, of greater than 0.5%.
 21. Thecopolymer of claim 1, wherein the copolymer has a proportion ofinversely inserted propylene units based on 2,1 insertion of propylenemonomer in all propylene insertions, as measured by ¹³C NMR, of greaterthan 0.6%.
 22. The copolymer of claim 1, wherein the copolymer has aproportion of inversely inserted propylene units based on 1,3 insertionof propylene monomer in all propylene insertions, as measured by ¹³CNMR, of greater than 0.05%.
 23. The copolymer of claim 1, wherein thecopolymer has a proportion of inversely inserted propylene units basedon 1,3 insertion of propylene monomer in all propylene insertions, asmeasured by ¹³C NMR, of greater than 0.07%.
 24. The copolymer of claim1, wherein the copolymer has a proportion of inversely insertedpropylene units based on 1,3 insertion of propylene monomer in allpropylene insertions, as measured by ¹³C NMR, of greater than 0.085%.25. The copolymer of claim 1, wherein the copolymer has anintermolecular tacticity such that at least 75% by weight of thecopolymer is soluble in two adjacent temperature fractions of a thermalfractionation carried out in hexane in 8° C. increments.
 26. Thecopolymer of claim 1, wherein the copolymer has an intermoleculartacticity such that at least 90% by weight of the copolymer is solublein two adjacent temperature fractions of a thermal fractionation carriedout in hexane in 8° C. increments.
 27. The copolymer of claim 1, whereinthe copolymer has an intermolecular tacticity such that at least 97% byweight of the copolymer is soluble in two adjacent temperature fractionsof a thermal fractionation carried out in hexane in 8° C. increments.28. The copolymer of claim 1, wherein the copolymer has a reactivityratio product r₁r₂ of less than 1.5.
 29. The copolymer of claim 1,wherein the copolymer has a molecular weight distribution Mw/Mn of from1.5 to
 5. 30. The copolymer of claim 1, wherein the copolymer has asolid state ¹H NMR relaxation time of less than 18 ms.
 31. The copolymerof claim 1, wherein the elasticity is less than 30%.
 32. The copolymerof claim 1, wherein the 500% tensile modulus is greater than 0.5 MPa.33. A metallocene-catalyzed copolymer comprising 5 to 25% by weight ofethylene-derived units and 95 to 75% by weight of propylene-derivedunits and substantially free of diene-derived units, the copolymerhaving: (a) a melting point of less than 90° C.; (b) a relationship ofelasticity to 500% tensile modulus such that Elasticity ≦0.935M+12, where elasticity is in percent and is less than 30% and M is the 500%tensile modulus in MPa; (c) a relationship of flexural modulus to 500%tensile modulus such that Flexural Modulus ≦4.2e ^(0.27M)+50,  whereflexural modulus is in MPa and M is the 500% tensile modulus in MPa; (d)a heat of fusion of from 1.0 J/g to 40 J/g; and (e) a molecular weightdistribution Mw/Mn of 1.5-5;
 34. The copolymer of claim 33, wherein thecopolymer comprises 6 to 20% by weight of ethylene-derived units and 94to 80% by weight of propylene-derived units.
 35. The copolymer of claim33, wherein the copolymer comprises 8 to 20% by weight ofethylene-derived units and 92 to 80% by weight of propylene-derivedunits.
 36. The copolymer of claim 33, wherein the copolymer comprises 10to 20% by weight of ethylene-derived units and 90 to 80% by weight ofpropylene-derived units.
 37. The copolymer of claim 33, wherein themelting point is between 25 and 90° C.
 38. The copolymer of claim 33,wherein the melting point is between 35 and 80° C.
 39. The copolymer ofclaim 33, wherein the melting point is between 45 and 70° C.
 40. Thecopolymer of claim 33, wherein the relationship of elasticity to 500%tensile modulus is: Elasticity ≦0.935M+6.
 41. The copolymer of claim 33,wherein the relationship of elasticity to 500% tensile modulus is:Elasticity ≦0.935M.
 42. The copolymer of claim 33, wherein therelationship of flexural modulus to 500% tensile modulus is: FlexuralModulus ≦4.2e ^(0.27M)+30.
 43. The copolymer of claim 33, wherein therelationship of flexural modulus to 500% tensile modulus is: FlexuralModulus ≦4.2e ^(0.27M)+10.
 44. The copolymer of claim 33, wherein therelationship of flexural modulus to 500% tensile modulus is: FlexuralModulus ≦4.2e ^(0.27M)+2.
 45. The copolymer of claim 33, wherein theheat of fusion is from 1.5 J/g to 30 J/g.
 46. The copolymer of claim 33,wherein the copolymer has a triad tacticity as determined by ¹³C NMR ofgreater than 75%.
 47. The copolymer of claim 33, wherein the copolymerhas a triad tacticity as determined by ¹³C NMR of greater than 85%. 48.The copolymer of claim 33, wherein the copolymer has a triad tacticityas determined by ¹³C NMR of greater than 90%.
 49. The copolymer of claim33, wherein the copolymer has a tacticity index m/r of from 4 to
 12. 50.The copolymer of claim 33, wherein the copolymer has a tacticity indexm/r of from 6 to
 10. 51. The copolymer of claim 33, wherein thecopolymer has a proportion of inversely inserted propylene units basedon 2,1 insertion of propylene monomer in all propylene insertions, asmeasured by ¹³C NMR, of greater than 0.5%.
 52. The copolymer of claim33, wherein the copolymer has a proportion of inversely insertedpropylene units based on 2,1 insertion of propylene monomer in allpropylene insertions, as measured by ¹³C NMR, of greater than 0.6%. 53.The copolymer of claim 33, wherein the copolymer has a proportion ofinversely inserted propylene units based on 1,3 insertion of propylenemonomer in all propylene insertions, as measured by ¹³C NMR, of greaterthan 0.05%.
 54. The copolymer of claim 33, wherein the copolymer has aproportion of inversely inserted propylene units based on 1,3 insertionof propylene monomer in all propylene insertions, as measured by ¹³CNMR, of greater than 0.07%.
 55. The copolymer of claim 33, wherein thecopolymer has a proportion of inversely inserted propylene units basedon 1,3 insertion of propylene monomer in all propylene insertions, asmeasured by ¹³C NMR, of greater than 0.085%.
 56. The copolymer of claim33, wherein the copolymer has an intermolecular tacticity such that atleast 75% by weight of the copolymer is soluble in two adjacenttemperature fractions of a thermal fractionation carried out in hexanein 8° C. increments.
 57. The copolymer of claim 33, wherein thecopolymer has an intermolecular tacticity such that at least 90% byweight of the copolymer is soluble in two adjacent temperature fractionsof a thermal fractionation carried out in hexane in 8° C. increments.58. The copolymer of claim 33, wherein the copolymer has anintermolecular tacticity such that at least 97% by weight of thecopolymer is soluble in two adjacent temperature fractions of a thermalfractionation carried out in hexane in 8° C. increments.
 59. Thecopolymer of claim 33, wherein the copolymer has a reactivity ratioproduct r₁r₂ of less than 1.5.
 60. The copolymer of claim 33, whereinthe copolymer has a solid state ¹H NMR relaxation time of less than 18ms.
 61. The copolymer of claim 33, wherein the 500% tensile modulus isgreater than 0.5 MPa.